1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a backlight unit for preventing abrasion of a surface of an optical sheet.
2. Discussion of the Related Art
A liquid crystal display device (hereinafter, referred to as ‘LCD’) is a flat panel display device that displays a picture by controlling the transmittance of light according to a video signal. Because LCDs are light in weight, thin, and have low power consumption, LCDs are used in an increasing number of applications. LCDs are used as the display devices for equipment such as notebook computers and office automation equipment. The LCD is being actively developed to produce displays having larger screens, higher resolutions, and lower power consumption to meet the demands of users.
FIG. 1 is a diagram representing a module of a direct type liquid crystal display device of the related art.
Referring to FIG. 1, the liquid crystal display module of the related art includes a board assembly 21 having a liquid crystal display panel 2 and polarizing sheets 8, 18 formed on front and rear surfaces of the liquid crystal display panel 2; a backlight unit that receives power from an external power source to irradiate light to the liquid crystal display panel 2; and a guide panel 4 installed between the liquid crystal display panel 2 and the backlight unit to support the liquid crystal display panel 2 and to be joined with the side surface of a support side bottom 16.
The liquid crystal display panel 2 has liquid crystal cells arranged in a matrix between upper and lower glass substrates. A thin film transistor (hereinafter, referred to as ‘TFT’) is included at each liquid crystal cell for switching a data signal in each of the liquid crystal cells. A refractive index of each liquid crystal cell is changed in accordance with a data signal, to thereby display a picture corresponding to the data signal. A tape carrier package (TCP) is attached onto the lower substrate of the liquid crystal display panel 2. A driver integrated circuit is mounted on the TCP to apply a drive signal to the thin film transistors. Further, the polarizing sheets 8 and 18 are respectively installed on the front and rear surfaces of the liquid crystal display panel 2. The polarizing sheets 8 and 18 function to improve a viewing angle for images displayed by the liquid crystal cells.
The backlight unit is formed at a lower part of the panel, and includes a plurality of light sources 36 receiving power from an external power source to emit light; a reflection sheet 14 disposed near the rear surface of the light source 36; a plurality of optical sheets 10 for increasing the portion of the light emitted by the light source 36 to illuminate the liquid crystal display panel 2; a cover bottom assembly 22 of a quadrangular shape which houses the light source, the reflection sheet, and other components.
The light source 36 includes a high voltage electrode and a low voltage electrode formed at respective ends of a glass tube; a high voltage wire soldered to the high voltage electrode; and a low voltage wire soldered to the low voltage electrode. Herein, the electrodes are encompassed by a holder of an insulating material.
The optical sheets 10 act to evenly disperse the light from the surface of the optical sheet 10 and to direct the travel path of the light towards the front of the liquid crystal display panel 2.
The inner side surface of an edge of the guide panel 4 is formed to safely receive the liquid crystal display panel 2, and a side wall of the guide panel guides the side surface of the liquid crystal display panel 2.
The cover bottom assembly 22 includes a cover bottom 20 where side wall surfaces are formed in two long sides thereof; and a supporter side bottom 16 where inclined side wall surfaces are formed in two short sides thereof. Accordingly, the cover bottom assembly 22 has side walls formed in the four sides to hold the liquid crystal display panel 2 and the optical sheets.
FIG. 2A is a diagram representing a cross section of a combining part (A) of the related art for joining the optical sheets 10 of the liquid crystal display module with the support side bottom 16. FIG. 2B is a perspective plan view of the combining part (A).
Referring to FIGS. 2A and 2B, there is formed a combining part (A) for joining the support main of the optical sheets 10 with the support side bottom 16 in one or both sides of the two side walls of the support side bottom 16. The structure of the combining part includes an opening 19 formed in the optical sheets 10 to join with a combining rod 17 formed in the support side bottom 16. The hole 19 of the optical sheets 10 is formed to have a side longer than the cylindrically shaped combining rod 17 formed in the support side bottom 16, so that the optical sheets 10 are not held in a fixed position on the support side bottom 16, but may move freely. The optical sheets 10 are allowed to move freely so that deformation to the optical sheets 10 resulting from heating or other physical effects does not generate wrinkles disturbing the flatness of the optical sheets 10. The flatness of the optical sheets 10 allows the optical sheets 10 to properly control the path of light.
In a structure where the optical sheets 10 are able to move freely, the individual optical sheets can rub against each other. Friction generated by the relative motion of individual optical sheets can result in the surface of the optical sheets being worn away and a prism on a prism sheet for controlling the path of light might be damaged. The damage of the prism on the prism sheet deteriorates brightness uniformity.
The above described problems can result in deterioration of a display quality of the liquid crystal display device.